This invention relates generally to electron beam apparatus as used in the fabrication of semiconductor integrated circuits and like microminiature devices, and more particularly the invention relates to a method of aligning electron beam equipment.
It has long been known that the high resolution and excellent depth of focusing capabilities of an electron beam make it a practical tool for inclusion in an automated system for manufacturing microminiature electronic devices. The electron beam is controlled in a highly accurate and high speed manner to expose an electron-resist-coated material as a step in the fabrication of extremely small and precise low cost integrated circuits.
Although an electron beam can be deflected and blanked in a high speed manner, the area over which the beam is capable of being deflected is relatively small. A basic problem presented, therefore, is accommodating this small area scan field in the rapid and efficient exposure of relatively large resist coated areas as is desirable with increasingly larger semiconductor wafers. In addition to larger areas to be exposed, increased densities of circuit elements are desired in semiconductor integrated circuits. A trend in the industry has been a greater number of circuits per unit of area and a tendency towards smaller and smaller circuits. In this manner, it becomes increasingly possible to integrate an entire subsystem or system on a relatively few number of semiconductor chips.
In copending application Ser. No. 847,485, filed Nov. 1, 1977, for "Electron Beam Exposure System Method and Apparatus" now U.S. Pat. No. 4,147,937 issued Apr. 3, 1979, an electron beam exposure system is disclosed. An electron beam column including electron source, blanking unit, deflection unit, and work chamber is provided along with an X-Y table and attendant controls for the electron beam column and table. The electron beam is accurately deflectible along X-Y axes over a small area (e.g. 512 microns square). Since the semiconductor wafer is much larger, the wafer and X-Y table on which the wafer is mounted must be repositioned many times for the wafer to be fully exposed to the electron beam. Moreover, the semiconductor substrate will be taken from and returned to the electron beam apparatus several times during the fabrication process for different electron beam mask definition patterns.
Thus, the need exists for accurately aligning and realigning the electron beam, work piece, and X-Y table during fabrication of a microminiature device using electron beam defined manufacturing masks.